System for preventing film fire in motion-picture projectors



Jan. 4, 1949. F. s. GROSZ, 55R 2,453,361

SYSTEM FOR PREVENTING FILM FIRE IN MOTION PICTURE PROJECTORS Filed Feb. 17, 1.948 5 Sheets-Sheet 1 2x83 gs O rim-* INSULAT/OWD I 3 l/Vsl/LQQT/QAV A i i a gwuem fo b FRANCIS 8. 6220321 SR.

- w mmza Jan 4, 1949'. F B GRQSZ, 59 2,453,161

SYSTEM FOR PREVENTING FILM FIRE IN MOTION PICTURE PROJECTORS Filfid Feb. 17, 1948 5 Sheets-Sheet 2 a vw M1404,

FRANCIS B. Gnosz,

JGM

1949- F. B. GROSZ, SR 2,458,161

SYSTEM FOR PREVENTING FILM FIRE IN MOTION PICTURE PROJECTORS 33"?- fawl attorneys 1949. F'. B. GROSZ, SR 2,458,161

SYSTEM FOR PREVENTING FILM FIRE] IN MOTION PICTURE PROJECTORS Filed Feb. 17, 1948 5 Sheets-Sheet 4 INSl/ 770 FRANCIS B. GRosZ,

Jan. 4, 1949. F. B. GROSZ, SR 2,453,161

SYSTEM FOR PREVENTING FILM FIRE IN MOTION PICTURE PROJECTORS Filed Feb. 17, 1948 5 Sheets-Sheet 5 Patented Jan. 4, 1949 SYSTEM FOR PREVENTING FILM FIRE IN MOTION-PICTURE PROJECTORS Francis B. Grosz, Sr., New Orleans, La.

Application February 17, 1948, Serial No. 8,886

Claims.

1 The invention has particular reference to a system for preventing film fire in a motion picture projector by automatically inserting a dowser plate or shutter between the light source and the film strip, but may be used with equal facility for automatically stopping a motion picture camera when the film strip breaks.

In the operation of a motion picture projector, if the film for any reason comes to rest, the intense light from the projecting .source remains focused on the stationary film and soon generates enough heat on the film to cause it to burst into flame. It has been the practice to depend on the vigilance of the projection machine operator to shut oil the light whenever any difiiculty is experienccd and before the film gets hot enough to catch fire.

The motion of the film past the aperture may be arrested, and therefore present a fire hazard, as a result of several kinds of failure. One is the stoppage of the projector mechanism. Breakage of the film is a more common type of failure. Sometimes the film tears longitudinally so that a strip of the film piles up" in the projector and presents a serious fire hazard.

It is therefore the principal object of this in vention to provide an automatic system for interrupting the projection beam of light whenever a failure occurs that would result in a film fire hazard.

In persuance of this object and many other objects that will be apparent to those skilled in the art, I provide a control means which is responsive to the several possible types of failure, and which is operative to release a dowser to block the path of the projection light. Projectors are commonly operated in pairs so that when the end of the reel of film is reached on one machine, the other machine carrying the following reel may be immediately put into operation without any interruption of the image on the screen. Since the sources of light used in projectors do not lend themselves to being quickly extinguished, it is the practice to use a solenoid-operated change-over dowser as a shutter when changing over from one machine to the other. By employing the change-over dowser, my invention may be added to projection machines within a minimum of expense and trouble compared with the value of the fire protection obtained.

Briefly, my'invention contemplates providing a disk or cylinder having electrical contact segments thereon, the disk or cylinder being driven by an idling film sprocket disposed in the projector mechanism and rotated with a jerky motion by the film. At least one other segmented disk or cylinder is provided and driven at constant speed by the projectors upper feed sprocket or lower take-up sprocket. Brushes riding on the segmented disks or cylinders are connected and arranged in such a way, in conjunction with relays, that improper operation on the machine, as when the film breaks, is immediately detected and the solenoid-operated dowser is deenergized. The beam of light is thus interrupted and the danger of film fire is eliminated.

Referring briefly to the drawings wherein I show application of my invention,

Figures 1 and 1A are a schematic diagram of one form of the invention;

Figure 2 is a perspective view showing a mechanical structure for one of the rotary switches used in the invention;

Figure 3 is a simplified schematic alternate diagram of the invention, and

Figure 4 is a diagrammatic elevational view of the essential parts of a motion picture projector with which the invention is used.

Referring now in greater detail to the drawings, a basic preliminary understanding of the invention can best be obtained from an explanation of Figures 3 and 4. Figure 4 shows a standard motion picture projector having a source of light iii, film trap H, film trap door l2, and lens system IS. The film trap H is provided with a driven intermittent motion sprocket wheel II and an idling sprocket wheel I4 on shaft 2i These sprocket wheels have sixteen teeth 15 or. each end for engagement with corresponding holeson the sides of the film 3. The intermittent sprocket wheel i3 is driven with a jerk; motion moving a quarter of a revolution each time, or to an extent corresponding to the distance between centers of successive picture frames on the film. Wheel l3 draws the film past the aperture I! on the film trap II at the rate of about 2| frames per second.

The film l6 drawn by intermittent sprocket l3 passes over idling sprocket l4 and imparts the same intermittent motion thereto-so long as the film between the two sprockets is not broken.

While the intermittent sprocket wheel l3 draws the film past the aperture one frame at a time, the upper feed sprocket l8 on shaft 28 and the lower take-up sprocket is are driven at a continuous rate and make one complete revolution in the same time that the intermittent sprocket l3 and idling sprocket I4 make a complete revolution in four jerks.

A dowser, generally designated 20, consists of a shutter plate 2| secured to an armature 22, one end of which is free to reciprocate axially in solenoid 23. When energized, solenoid 23 holds the shutter plate 2| up, and when de-energized, the shutter plate is allowed to fall into the path of light between the source l8 and the film IS. The electrical system, to be described, is operative to keep the solenoid 23 energized until through some failure of the projector or breakage of the film, a film fire hazard is created.

Referring now to Figure 3 which is a highly simplified form of the invention, shaft 24 is the shaft carrying the idling sprocket wheel M of Figure 4, and broken shaft 28 is the shaft carrying the upper feed sprocket l8 of Figure 4. The

shaft 29 of Figure 4 carrying lower take-up sprocket l8 may be employed in place of shaft 28 if desired.

Shaft 24 has secured to the end thereof a rotary contact disk, generally designated 38, having a plurality of contact segments thereon separated by an insulating material 3 I. Disk 38, being connected by shaft 24 to idling sprocket I4, moves a quarter of a revolution at a time corresponding with the movement of the film from one frame to the next.

Shaft 28 has secured thereto three rotary contact disks generally designated 48, 58 and 88, having contact areas 4|, 5| and GI, respectively, and insulating areas 42, 52 and 62, respectively. Disks 48-, 58 and 88, being connected to shaft 28, rotate with a continuous motion making one revolution for each four quarter revolutions of disk 38.

It is to be understood that all the solenoids in the drawings are provided with electrical returns to the source by ground or wires, which returns have been omitted from the drawings in order to avoid crowding and confusion.

Electricity is supplied to dowser 28 from the positive side of source 18 through wire 1 I, relay 12, wire 15, relay 15, wire 19, relay 88, wire 82, relay 83 and wire 85, and back through ground to the negative side of source 18. During normal operation of the projector, the relays remain in closed position as shown and solenoid 23 of dowser 28 remains energized.

During normal operation, relay 16 is kept in the closed'position as follows: When disk 38 is at rest between motions, current is supplied from source 18 through wire 32, brush 33, contact sector 34, and brush 35 to solenoid 18. When disk 38 makes a rapid quarter revolution, disk 48 has rotated a fraction of a revolution from the position shown in Figure 3, and current is supplied from source 18 through wire 43, brush 44, contact plate 4|, brush 45, and wire 48 to solenoid 17. The segments of contact plate 4| cause the relay 16 to be energized whenever disk 38 is in motion and not energizing relay 16. If the film strip l8 breaks and disk 38 comes to rest with brushes 33 and 35 on the insulating portion 3| of the disk, current will not be allowed to pass from the source 18 to solenoid I8, relay 16 will open, and dowser solenoid 23 will be de-energized thereby allowing the shutter plate 2| to fall into the path of the light beam and prevent the film from catching fire.

On the other hand, if the film breaks and disk 38 comes to rest with brushes 33 and 35 resting on one of the contact segments 34, current will continue to pass from the source 18 to solenoid l8 and relay 18 will remain closed. Under these conditions the dowser solenoid 23 would not be de-energized. Relay l2 and disks 58 and 88 provide for such a contingency in the following manner: Disks 58 and 68 are on the same shaft 28 as disk and rotate at constant speed. Current is supplied from source 18 through wire 32, brush 53, contact plate 5| and brush 54 to solenoid 14 at I all times except when brush 54 is on an insulating segment 52, i. e., at all times that disk 38 is rotating or should be rotating. If disk 38 has come to rest in a position such as shown, relay 12 will be de-energized when insulating segment 52 of disk 58 passes under brush 54 and dowser solenoid 23 will be de-energized thus cutting off the beam of light.

Under normal conditions of operation (when the film strip is unbroken) relay 12 will be kept energized during the time that insulating segment 52 is under brush by the flow of current from source 18, through wire 32, brush 36, contact plate 31, brush 38, brush 83, contact plate BI and brush 64 to solenoid 13 of relay I2.

If, as the result of breakage of the film, disk 38 came to rest in a position such that contact segment 34 was under brushes 33 and 35 and at the same time contact segment 31 was under brush 38, the dowser would not be de-energized. To take care of this possibility, a brush 85 was provided riding on disk 68 and connected to solenoid 8| of relay 88. Brush 65 is displaced from brush 84 and when contact plate 8| comes around under brush 65, current is allowed to fiow from source 18, through wire 32, brush 38, contact plate 31, brush 38, brush83, contact plate 8| and brush 55 to solenoid 8|. When solenoid 8| is thus energized, relay 88 opens the circuit to the dowser solenoid 23 and the dowser shutter 2| interrupts the beam of light. It is to be noted that during normal operation, relay 8| is not actuated because brush 38 on disk 38 is not in contact with contact plate 31 at the same time that brush 65 on disk 88 is in contact with contact plate BI.

a of contact segment 31.

It is to be noted that brush 38 has associated therewith a brush 39 which is spaced from brush 38 by an amount slightly greater than the width Therefore, contact is made by brush 38 or 39 after only a small amount of rotation of disk 38.

Relay 83 is inserted in the circuit to the dowser solenoid 23 and is provided with a holding coil 84 connected on one side to wire 85 and on the other side to ground. Relay 83 is provided for the purpose of permanently opening the circuit to the dowser solenoid 23 whenever any one of relays 12, 16 and 88 is'momentarily opened. Without relay 83, the dowser solenoid 23 would be alternately energized and de-energized after a breakage of the film by reason of the opening and closing of relay 18 as disk 48 continued to rotate. In the embodiment of the invention shown in Figures 1 and 1A, provisions are made for automatically re-setting relay 88. l

The embodiment of the invention shown in Figures 1 and 1A is similar to the simplified embodiment previously described and shown in Figure 3 with the following exceptions: Disk 38' is divided into sixteen contact segments, one corresponding to each tooth of the standard film sprocket wheel; a system of relays is inserted electrically between disk 38' and relay l6; relay 83' is provided with resetting means, and means are provided for de-energizing the dowser when the film tears longitudinally in such a way that the sprocket wheels continue-to rotate in the normal Way, V

In the just mentioned Figures 1 and 1A, disk 38' is shown diagrammatically to be divided into an outer ring of sixteen segments 34' which are designated, in order, A, B, C, D, A, B, etc. The four'segments designated A are in contact with wire A. Ihe other segments are similarly connected to wires B, C and D. An inner row of sixteen contact segments 31' are all connected together in the center. Reference should be made to Figure 2 for a structural form of disk 30' having the contact segments arranged on the peripheral edge of the disk segments 34 and conshown, current flows from the positive source through brush 33, contact segment B, wire I20, relay I 2|, and wire 92 to solenoid I8 of relay I6. After the next quarter revolution of disk 30', brush 33 will be in contact with the next successive segment B, and so on.

In the event that film failure causes the opening of one of relays I2, I6 or 80, solenoid v.iIi of relay 83' will be de-energized and armature 93 will fall to its lower position under pawl 94 and in contact with wire 95. When the film failure has been rectified and the projector is again put in operation, relay t3 will be automatically reset in the following way: Current is supplied from source Iii through the various relays, wire 82, solenoid til and also through armature 93 and wire 95 to solenoids H2, H6, I22, I26, I532, I38, Hi2 and I46. As a result of the energizing oi relays iii, I'M, iti and MI, pulses of current are supplied during the next quarter revolution of disk 38' from four segments A, B, C and D, through wires lit, I2Il, I38 and MB, respectively, to pawl solenoids III, I2l, IBI and MI, respectively. Armatures H8, I28, I38 and I48 are then free to be drawn upwardly allowing current to fiow during the next rotation of disk 3% from the source through brush 33, segment B (or A, C or D), brush 35, wire Hi9, armature Hi8, wire I39, armature ieb wire I29, armature I28, wire IIL armature lit and wire 96 to pawl solenoid 9i. Pawl 94, then releases armature 93 and allows it to be drawn up by solenoid 90 thereby again completing the circuit to the dowser solenoid 23.

- In the operation of a motion picture projector, the film sometimes begins to tear transversely and then continues to tear longitudinally down the middle. Under these conditions, the perforations on one side of the film strip remain in engagement with the teeth on the corresponding side of the sprocket wheels-and sprocket wheel I4 continues to rotate with the normal intermittent motion. Relay I60 is inserted in the wire 85 going to the dowser solenoid 23 for the purpose of de-energizing the dowser when the film tears longitudinally. Metallic spring fingers I83 are disposed" in such a way that the film strip passes between the film trap II and the fingers I63, thereby insulating the fingers from the film trap during normal operating'conditions. Fingers I63 are connected by wire I64 through solenoid I8I of relay I60, and through switch I65 to source of electricity I66. Film trap III is connected by wire I61 to source of electricity I66. Whenever the film tears, electrical contact is made between the fingers I63 and film trap II, thereby energizing relay I and de-energizing dowser solenoid 23. It may be observed that if the power supply III is the same power supply used to drive the projector or camera, a failure of the power supply automatically releases the shutter 2 I.

It is apparent that I have provided a foolproof means for de-energizing the dowser solenoid whenever there is a failure of any kind that causes the him or a portion thereof to remain stationary in the path of light fromthe source.

My invention may also be applied to electrically driven motion picture cameras, for the purpose of automatically stopping the camera before a large amount of film is destroyed by tearing. This is so because cameras have idling and constant speed sprockets which operate in the same way as sprockets in projectors, and hence the invention may be used with facility and in a manner believed obvious to interrupt the source of electricity to a camera when there is a film failure for the purpose just stated.

While I have described and illustrated specifically the invention, it is to be understood that various changes may be made in the invention, within the scope of the appended claims,

What I claim is:

1. In a motion picture projector having a solenoid-operated change-over dowser, a control circuit for preventing film fire comprising a rotary switch driven by the idling film sprocket of the projector, a second rotary switch driven by a constant speed film sprocket of the projector, a source of electricity for energizing the solenoidoperated dowser, and relay means responsive to the relative rotation of said rotary switches and operative to interrupt said source of electricity for the dowser.

. 2. In a motion picture projector, an apparatus for preventing film fire comprising a solenoidoperated dowser and a source of electrical energy therefor, switch means operated by the idling film sprocket of the projector, a second switch means operated by a constant speed film sprocket of the projector, and means responsive to the cyclical operation of said switches and operative to interrupt the energy to the dowser when the cycle of operation is changed.

3. In a motion picture projector having a solenoid-operated dowser and a source of electricity therefor, a control means for said dowser comprising a rotary switch driven by the idling film sprocket of the projector, the idling sprocket being driven with an intermittent motion by the film strip, a second rotary switch driven at constant speed by a content speed film sprocket of the projector, the second switch being operative in conjunction with the first to interrupt the current from the source to the dowser when a film failure stops the synchronized rotation of the first switch.

4. In a motion picture projector having a. solenoid-operated dowser and an electrical source therefor, a control for the dowser comprising a rotary member driven by the idling sprocket wheel of the projector and having a plurality of contact segments, a second rotary member driven by a constant speed sprocket of the projector and having a plurality of contact segments, and means including brushes riding on the rotary members for actuating the dowser when the rotary members get out of synchronism as a result of film failure.

5. In a motion picture. machine operated from a source of electricity, 9. control circuit for interrupting the source of electricity comprising rotary switch means driven by the idling film sprocket of the machine, a second rotary switch means driven by a constant speed film sprocket in the machine, and meansresponsive to the cyclical operation of said switches and operative to interrupt the source of electricity to the machine when film strip failure stops the normal cyclical operation of said switches.

FRANCIS B. GROSZ, SR.

REFERENCES CITED The following references are of record in the file of this patent:

Number 10 Number 8 UNITED STATES PA'I'E'NI'S Name Date Lick July 22, 1924 Brook Apr. 7, 1931 Scheinfeld Apr. 17, 1934 Sebastiani Nov. 8, 1938 FOREIGN PATENTS Country Date Italy Apr. 30, 1929 

